Catalyst composition and process for controlling the characteristics of conjugated diene polymers

ABSTRACT

A catalyst composition that is the combination of or the reaction product of ingredients including an iron-containing compound, a hydrogen phosphite, and a mixture of two or more organoaluminum compounds. This catalyst composition is particularly useful for polymerizing conjugated dienes. When this catalyst composition is used to polymerize 1,3-butadiene into syndiotactic 1,2-polybutadiene the ratio of the organoaluminum compounds can be adjusted to vary the melting temperature and molecular weight of the polymer product.

This is a continuation of application Ser. No. 09/475,345, filed on Dec.30, 1999, now U.S. Pat. No. 6,288,183.

FIELD OF THE INVENTION

The present invention generally relates to a process for polymerizingconjugated dienes. More particularly, the process of the presentinvention employs a catalyst composition that is formed by combining aniron-containing compound, a hydrogen phosphite, and a blend of two ormore sterically distinct organoaluminum compounds. By utilizing thiscatalyst composition, the characteristics, such as the meltingtemperature, of the resulting conjugated diene polymers can bemanipulated. The preferred embodiments of the present invention aredirected toward a process for polymerizing 1,3-butadiene intosyndiotactic 1,2-polybutadiene whereby the melting temperature of theresulting polymer can be controlled.

BACKGROUND OF THE INVENTION

Syndiotactic 1,2-polybutadiene is a crystalline thermoplastic resin thathas a stereoregular structure in which the side chain vinyl groups arelocated alternately on the opposite sides in relation to the polymericmain chain. Syndiotactic 1,2-polybutadiene is a unique material thatexhibits the properties of both plastics and rubber, and therefore ithas many uses. For example, films, fibers, and various molded articlescan be made from syndiotactic 1,2-polybutadiene. It can also be blendedinto and co-cured with natural or synthetic rubber.

Syndiotactic 1,2-polybutadiene can be made by solution, emulsion orsuspension polymerization. The physical properties of syndiotactic1,2-polybutadiene are largely determined by its melting temperature andmolecular weight. Generally, syndiotactic 1,2-polybutadiene has amelting temperature within the range of about 195° C. to about 215° C.,but due to processability considerations, it is generally desirable forsyndiotactic 1,2-polybutadiene to have a melting temperature of lessthan about 195° C. Accordingly, there is a need for means to regulatethe melting temperature and molecular weight of syndiotactic1,2-polybutadiene.

Various transition metal catalyst systems based on cobalt, titanium,vanadium, chromium, and molybdenum for the preparation of syndiotactic1,2-polybutadiene have been reported. The majority of these catalystsystems, however, have no practical utility because they have lowcatalytic activity or poor stereoselectivity, and in some cases theyproduce low molecular weight polymers or partially crosslinked polymersunsuitable for commercial use.

The following two cobalt-based catalyst systems are well known for thepreparation of syndiotactic 1,2-polybutadiene on a commercial scale: (1)a system containing cobalt bis(acetylacetonate), triethylaluminum,water, and triphenylphosphine (U.S. Pat. Nos. 3,498,963 and 4,182,813),and (2) a system containing cobalt tris(acetylacetonate),triethylaluminum, and carbon disulfide (U.S. Pat. No. 3,778,424). Thesecobalt-based catalyst systems also have disadvantages.

The first cobalt catalyst system referenced above yields syndiotactic1,2-polybutadiene having very low crystallinity. Also, this catalystsystem develops sufficient catalytic activity only when halogenatedhydrocarbon solvents are used as the polymerization medium, andhalogenated solvents present toxicity problems.

The second cobalt catalyst system referenced above uses carbon disulfideas one of the catalyst components. Because of its low flash point,obnoxious smell, high volatility, and toxicity, carbon disulfide isdifficult and dangerous to use, and requires expensive safety measuresto prevent even minimal amounts escaping into the atmosphere.Furthermore, the syndiotactic 1,2-polybutadiene produced with thiscobalt catalyst system has a very high melting temperature of about200-210° C., which makes it difficult to process the polymer. Althoughthe melting temperature of the syndiotactic 1,2-polybutadiene producedwith this cobalt catalyst system can be reduced by employing a catalystmodifier as a fourth catalyst component, the presence of this catalystmodifier has adverse effects on the catalyst activity and polymeryields. Accordingly, many restrictions are required for the industrialutilization of these cobalt-based catalyst systems.

Coordination catalyst systems based on iron-containing compounds, suchas the combination of iron(III) acetylacetonate and triethylaluminum,have been known for some time, but they have shown very low catalyticactivity and poor stereoselectivity for the polymerization of1,3-butadiene. The product mixture often contains oligomers, lowmolecular weight liquid polymers, and partially crosslinked polymers.Therefore, these iron-based catalyst systems have no industrial utility.

Because syndiotactic 1,2-polybutadiene is useful and the catalysts knownheretofore in the art have many shortcomings, it would be advantageousto develop a new and significantly improved catalyst composition thathas high activity and stereoselectivity for polymerizing 1,3-butadieneinto syndiotactic 1,2-polybutadiene. It would be additionallyadvantageous if that catalyst system was versatile enough to control themelting temperature and molecular weight of the polymerization product.

SUMMARY OF THE INVENTION

In general, the present invention provides a process for preparingconjugated diene polymers with desired characteristics comprising thestep of polymerizing conjugated diene monomers in the presence of acatalytically effective amount of a catalyst composition formed bycombining (a) an iron-containing compound, (b) a hydrogen phosphite, and(c) a blend of two or more sterically distinct organoaluminum compounds.

The present invention also provides a method for controlling the meltingtemperature of a crystalline conjugated diene polymer that is preparedby polymerizing conjugated diene monomers with a catalyst compositionthat is formed by combining (a) an iron-containing compound, (b) ahydrogen phosphite, and (c) a blend of two or more sterically distinctorganoaluminum compounds, the method comprising the steps of selectingat least one sterically hindered organoaluminum compound; selecting atleast one sterically non-hindered organoaluminum compound; combining theselected organoaluminum compounds to form ingredient (c) of the catalystcomposition; and thereafter polymerizing the conjugated diene monomerswith the catalyst composition.

The present invention also provides a catalyst composition formed by aprocess comprising the step of combining (a) an iron-containingcompound, (b) a hydrogen phosphite, and (c) a blend of two or moresterically distinct organoaluminum compounds.

Advantageously, the catalyst composition utilized in the presentinvention has very high catalytic activity and stereoselectivity forpolymerizing conjugated diene monomers such as 1,3-butadiene. Thisactivity and selectivity, among other advantages, allows conjugateddiene polymers, such as syndiotactic 1,2-polybutadiene, to be producedin very high yields with low catalyst levels after relatively shortpolymerization times. Significantly, the catalyst composition of thisinvention is very versatile. By blending sterically distinctorganoaluminum compounds, it is possible to produce crystallineconjugated diene polymers, such as syndiotactic 1,2-polybutadiene, witha wide range of melting temperatures and molecular weights, thuseliminating the need to add a melting temperature regulator or amolecular weight regulator that adversely affects the catalyst activityand the polymer yield. In addition, the catalyst composition utilized inthis invention does not contain carbon disulfide. Therefore, thetoxicity, objectionable smell, dangers, and expense associated with theuse of carbon disulfide are eliminated. Further, the catalystcomposition utilized in this invention is iron-based, and iron compoundsare generally stable, inexpensive, relatively innocuous, and readilyavailable. Furthermore, the catalyst composition utilized in thisinvention has a high catalytic activity in a wide variety of solventsincluding the environmentally-preferred nonhalogenated solvents such asaliphatic and cycloaliphatic hydrocarbons.

Other advantages and features of the present invention will be apparentfrom a consideration of the following detailed description of thepresent invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is generally directed toward a process forsynthesizing conjugated diene polymers by using an iron-based catalystcomposition. The preferred embodiments of this invention are directedtoward the synthesis of crystalline conjugated diene polymers, such assyndiotactic 1,2-polybutadiene. The iron-based composition is formed bycombining (a) an iron-containing compound, (b) a hydrogen phosphite, and(c) a blend of two or more sterically distinct organoaluminum compounds.It has now been found that the characteristics of the resultingconjugated diene polymer can be adjusted by selecting certain stericallydistinct organoaluminum compounds. For example, the melting temperatureof crystalline conjugated diene polymers can be adjusted by selectingcertain sterically distinct organoaluminum compounds or by varying themolar ratio of the sterically distinct organoaluminum compounds.

As noted above, the catalyst composition of the present invention isformed by combining (a) an iron-containing compound, (b) a hydrogenphosphite, and (c) a blend of two or more sterically distinctorganoaluminum compounds. In addition to the three catalyst ingredients(a), (b), and (c), other organometallic compounds or Lewis bases canalso be added, if desired.

Various iron-containing compounds or mixtures thereof can be employed asingredient (a) of the catalyst composition of this invention. It isgenerally advantageous to employ iron-containing compounds that aresoluble in a hydrocarbon solvent such as aromatic hydrocarbons,aliphatic hydrocarbons, or cycloaliphatic hydrocarbons.Hydrocarbon-insoluble iron-containing compounds however, can besuspended in the polymerization medium to form the catalytically activespecies and are therefore also useful.

The iron atom in the iron-containing compounds can be in variousoxidation states including but not limited to the 0, +2, +3, and +4oxidation states. It is preferable to use divalent iron compounds (alsocalled ferrous compounds), wherein the iron is in the +2 oxidationstate, and trivalent iron compounds (also called ferric compounds),wherein the iron is in the +3 oxidation state. Suitable types ofiron-containing compounds that can be utilized include, but are notlimited to, iron carboxylates, iron carbamates, iron dithiocarbamates,iron xanthates, iron β-diketonates, iron alkoxides, iron aryloxides, andorganoiron compounds.

Some specific examples of suitable iron carboxylates include iron(II)formate, iron(III) formate, iron(II) acetate, iron(III) acetate,iron(II) acrylate, iron(III) acrylate, iron(II) methacrylate, iron(III)methacrylate, iron(II) valerate, iron(III) valerate, iron(II) gluconate,iron(III) gluconate, iron(II) citrate, iron(III) citrate, iron(II)fumarate, iron(III) fumarate, iron(II) lactate, iron(III) lactate,iron(II) maleate, iron(III) maleate, iron(II) oxalate, iron(III)oxalate, iron(II) 2-ethylhexanoate, iron(III) 2-ethylhexanoate, iron(II)neodecanoate, iron(III) neodecanoate, iron(II) naphthenate, iron(III)naphthenate, iron(II) stearate, iron(III) stearate, iron(II) oleate,iron(III) oleate, iron(II) benzoate, iron(III) benzoate, iron(II)picolinate, and iron(III) picolinate.

Some specific examples of suitable iron carbamates include iron(II)dimethylcarbamate, iron(III) dimethylcarbamate, iron(II)diethylcarbamate, iron(III) diethylcarbamate, iron(II)diisopropylcarbamate, iron(III) diisopropylcarbamate, iron(II)dibutylcarbamate, iron(III) dibutylcarbamate, iron(II)dibenzylcarbamate, and iron(III) dibenzylcarbamate.

Some specific examples of suitable iron dithiocarbamates includeiron(II) dimethyldithiocarbamate, iron(III) dimethyldithiocarbamate,iron(II) diethyl-dithiocarbamate, iron(III) diethyldithiocarbamate,iron(II) diisopropyldithio-carbamate, iron(III)diisopropyldithiocarbamate, iron(II) dibutyldithiocarbamate, iron(III)dibutyldithiocarbamate, iron(II) dibenzyldithiocarbamate, and iron(III)di-benzyldithiocarbamate.

Some specific examples of suitable iron xanthates include iron(II)methylxanthate, iron(III) methylxanthate, iron(II) ethylxanthate,iron(III) ethylxanthate, iron(II) isopropylxanthate, iron(III)isopropylxanthate, iron(II) butylxanthate, iron(III) butylxanthate,iron(II) benzylxanthate, and iron(III) benzylxanthate.

Some specific examples of suitable iron β-diketonates include iron(II)acetylacetonate, iron(III) acetylacetonate, iron(II)trifluoroacetylacetonate, iron(III) trifluoroacetylacetonate, iron(II)hexafluoroacetylacetonate, iron(III) hexafluoroacetylacetonate, iron(II)benzoylacetonate, iron(III) benzoylacetonate, iron (II)2,2,6,6-tetramethyl-3,5-heptanedionate, and iron (III)2,2,6,6-tetramethyl-3,5-heptanedionate.

Some specific examples of suitable iron alkoxides or aryloxides includeiron(II) methoxide, iron(III) methoxide, iron(II) ethoxide, iron(III)ethoxide, iron(II) isopropoxide, iron(III) isopropoxide, iron(II)2-ethylhexoxide, iron(III) 2-ethylhexoxide, iron(II) phenoxide,iron(III) phenoxide, iron(II) nonylphenoxide, iron(III) nonylphenoxide,iron(II) naphthoxide, and iron(III) naphthoxide.

The term organoiron compound refers to any iron compound containing atleast one iron-carbon bond. Some specific examples of suitableorganoiron compounds include bis(cyclopentadienyl)iron(II) (also calledferro-cene), bis(pentamethylcyclopentadienyl)iron(II) (also calleddecamethylferrocene), bis(pentadienyl)iron(II),bis(2,4-dimethylpentadienyl)iron(II), bis(allyl)dicarbonyl-iron (II),(cyclopentadienyl)(pentadienyl)iron(II), tetra(1-norbomyl)iron(IV),(tri-methylenemethane) tricarbonyliron(II),bis(butadiene)carbonyliron(0), butadienetricarbonyliron(0), andbis(cyclooctatetraene)iron(0).

Useful hydrogen phosphite compounds that can be employed as ingredient(b) of the catalyst composition of this invention are acyclic hydrogenphosphites, cyclic hydrogen phosphites, and mixtures thereof.

In general, the acyclic hydrogen phosphites may be represented by thefollowing keto-enol tautomeric structures:

Where R¹ and R², which may be the same or different, are mono-valentorganic groups. Preferably, R¹ and R² are hydrocarbyl groups such as,but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl,cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl,aralkyl, alkaryl, and alkynyl groups, with each group preferablycontaining from 1 carbon atom, or the appropriate minimum number ofcarbon atoms to form the group, up to 20 carbon atoms. These hydrocarbylgroups may contain heteroatoms such as, but not limited to, nitrogen,oxygen, silicon, sulfur, and phosphorus atoms. The acyclic hydrogenphosphites exist mainly as the keto tautomer (shown on the left), withthe enol tautomer (shown on the right) being the minor species. Theequilibrium constant for the above-mentioned tautomeric equilibrium isdependent upon factors such as the temperature, the types of R¹ and R²groups, the type of solvent, and the like. Both tautomers may beassociated in dimeric, trimeric or oligomeric forms by hydrogen bonding.Either of the two tautomers or mixtures thereof can be employed.

Some representative and non-limiting examples of suitable acyclichydrogen phosphites are dimethyl hydrogen phosphite, diethyl hydrogenphosphite, dibutyl hydrogen phosphite, dihexyl hydrogen phosphite,dioctyl hydrogen phosphite, didecyl hydrogen phosphite, didodecylhydrogen phosphite, dioctadecyl hydrogen phosphite,bis(2,2,2-trifluoroethyl) hydrogen phosphite, diisopropyl hydrogenphosphite, bis(3,3-dimethyl-2-butyl) hydrogen phosphite,bis(2,4-dimethyl-3-pentyl) hydrogen phosphite, di-t-butyl hydrogenphosphite, bis(2-ethylhexyl) hydrogen phosphite, dineopentyl hydrogenphosphite, bis(cyclopropylmethyl) hydrogen phosphite,bis(cyclobutylmethyl) hydrogen phosphite, bis(cyclopentylmethyl)hydrogen phosphite, bis(cyclohexylmethyl) hydrogen phosphite,dicyclobutyl hydrogen phosphite, dicyclopentyl hydrogen phosphite,dicyclohexyl hydrogen phosphite, dimethyl hydrogen phosphite, diphenylhydrogen phosphite, dinaphthyl hydrogen phosphite, dibenzyl hydrogenphosphite, bis (1-naphthylmethyl) hydrogen phosphite, diallyl hydrogenphosphite, dimethallyl hydrogen phosphite, dicrotyl hydrogen phosphite,ethyl butyl hydrogen phosphite, methyl hexyl hydrogen phosphite, methylneopentyl hydrogen phosphite, methyl phenyl hydrogen phosphite, methylcyclohexyl hydrogen phosphite, methyl benzyl hydrogen phosphite, and thelike. Mixtures of the above dihydrocarbyl hydrogen phosphites may alsobe utilized.

In general, cyclic hydrogen phosphites contain a divalent organic groupthat bridges between the two oxygen atoms that are singly-bonded to thephosphorus atom. These cyclic hydrogen phosphites may be represented bythe following keto-enol tautomeric structures:

Where R³ is a divalent organic group. Preferably, R³ is a hydrocarbylenegroup such as, but not limited to, alkylene, cycloalkylene, substitutedalkylene, substituted cycloalkylene, alkenylene, cycloalkenylene,substituted alkenylene, substituted cycloalkenylene, arylene, andsubstituted arylene groups, with each group preferably containing from 1carbon atom, or the appropriate minimum number of carbon atoms to formthe group, up to 20 carbon atoms. These hydrocarbylene groups maycontain heteroatoms such as, but not limited to, nitrogen, oxygen,silicon, sulfur, and phosphorus atoms. The cyclic hydrogen phosphitesexist mainly as the keto tautomer (shown on the left), with the enoltautomer (shown on the right) being the minor species. The equilibriumconstant for the above-mentioned tautomeric equilibrium is dependentupon factors such as the temperature, the types of R³ group, the type ofsolvent, and the like. Both tautomers may be associated in dimeric,trimeric or oligomeric forms by hydrogen bonding. Either of the twotautomers or mixtures thereof can be used.

The cyclic hydrogen phosphites may be synthesized by thetransesterification reaction of an acyclic dihydrocarbyl hydrogenphosphite (usually dimethyl hydrogen phosphite or diethyl hydrogenphosphite) with an alkylene diol or an arylene diol. Procedures for thistransesterification reaction are well known to those skilled in the art.Typically, the transesterification reaction is carried out by heating amixture of an acyclic dihydrocarbyl hydrogen phosphite and an alkylenediol or an arylene diol. Subsequent distillation of the side-productalcohol (usually methanol or ethanol) that results from thetransesterification reaction leaves the new-made cyclic hydrogenphosphite.

Some specific examples of suitable cyclic alkylene hydrogen phosphitesare 2-oxo-(2H)-5-butyl-5-ethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-5,5-dimethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4-methyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-5-ethyl-5-methyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-5,5-diethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-5-methyl-5-propyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4-isopropyl-5,5-dimethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4,6-dimethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4-propyl-5-ethyl-1,3,2-dioxaphosphorinane,2-oxo-(2H)-4-methyl-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-dimethyl-1,3,2-dioxaphospholane,2-oxo-(2H)-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane, and the like.Mixtures of the above cyclic alkylene hydrogen phosphites may also beutilized.

Some specific examples of suitable cyclic arylene hydrogen phosphitesare 2-oxo-(2H)-4,5-benzo-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-(3′-methylbenzo)-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-(4′-methylbenzo)-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-(4′-tert-butylbenzo)-1,3,2-dioxaphospholane,2-oxo-(2H)-4,5-naphthalo-1,3,2-dioxaphospholane, and the like. Mixturesof the above cyclic arylene hydrogen phosphites may also be utilized.

As noted above, ingredient (c) of the catalyst composition of thepresent invention includes a blend of two or more organoaluminumcompounds that have distinct steric hindrance. In is generallyadvantageous to employ organoaluminum compounds that are soluble inhydrocarbon solvent. As used herein, the term “organoaluminum compound”refers to any aluminum compound containing at least one aluminum-carbonbond. In a preferred embodiment, ingredient (c) of the catalystcomposition utilized in this invention is formed by combining at leastone organoaluminum compound that is sterically hindered with at leastone organoaluminum compound that is sterically less hindered or, moresimply stated, non-hindered.

The organoaluminum compounds employed to form ingredient (c) aregenerally characterized by containing at least one organic group that isattached to an aluminum atom via a carbon atom. The structure of theseorganic groups determines whether the organoaluminum compound issterically hindered or non-hindered for purposes of this invention. Thestructures of these organic groups are best explained with reference tothe following figure, which shows an organic group attached to analuminum atom:

where C^(α) will be referred to as the α carbon and C^(β) will bereferred to as the β carbon. In general, the steric hindrance of anorganoaluminum compound is determined by the substitution patterns ofthe α and β carbons. An organoaluminum compound is sterically hinderedwhere the a carbon is secondary or tertiary, i.e., has only one or nohydrogen atom bonded thereto. Also, an organoaluminum compound ishindered where the β carbon has only one or no hydrogen atom bondedthereto. On the other hand, an organoaluminum compound is non-hinderedwhere the α carbon is primary, i.e., has two hydrogen atoms bondedthereto, and the β carbon has at least two hydrogen atoms bondedthereto. Other non-hindered organic groups include CH₃ or CH₂F.

Non-limiting examples of sterically hindered organic groups includeisopropyl, isobutyl, t-butyl, neopentyl, cyclohexyl,1-methylcyclopentyl, and 2,6-dimethylphenyl groups. Non-limitingexamples of non-hindered organic groups include methyl, ethyl, n-propyl,n-butyl, n-hexyl, and n-octyl groups.

Those skilled in the art will understand that an organoaluminum compoundmay include both hindered and non-hindered organic groups because thealuminum atom generally has a valence of three as shown in the foregoingfigure. In the event that the organoaluminum compound includes bothhindered and non-hindered organic groups, then, for purposes of thisspecification, the compound will be deemed to be both stericallyhindered and non-hindered because it is believed that both the hinderedand non-hindered organic groups will have an impact on thecharacteristics of the resulting polymer.

A preferred class of organoaluminum compounds that can be utilized toform ingredient (c) is represented by the general formulaAlR_(n)X_(3−n), where each R, which may be the same or different, is amono-valent organic group that is attached to the aluminum atom via acarbon atom, where n is an integer of 1 to 3, and where each X, isselected from a hydrogen atom, a carboxylate group, an alkoxide group,or an aryloxide group. Preferably, each R is a hydrocarbyl group suchas, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl,alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, allyl,substituted aryl, aralkyl, alkaryl, and alkynyl groups, with each grouppreferably containing from 1 carbon atom, or the appropriate minimumnumber of carbon atoms to form the group, up to about 20 carbon atoms.Also, these hydrocarbyl groups may contain heteroatoms such as oxygen,sulfur, nitrogen, silicon, and phosphorous atoms. Preferably, each X isa carboxylate group, an alkoxide group, or an aryloxide group, with eachgroup preferably containing from 1 carbon atom, or the appropriateminimum number of carbon atoms to form the group, up to about 20 carbonatoms.

Thus, some suitable types of organoaluminum compounds that can beutilized include, but are not limited to, trihydrocarbylaluminum,dihydrocarbylaluminum hydride, hydrocarbylaluminum dihydride,dihydrocarbylaluminum carboxylate, hydrocarbylaluminum bis(carboxylate),dihydrocarbylaluminum alkoxide, hydrocarbylaluminum dialkoxide,dihydrocarbylaluminum aryloxide, hydrocarbylaluminum diaryloxide, andthe like, and mixtures thereof. Trihydrocarbylaluminum compounds aregenerally preferred.

Some specific examples of organoaluminum compounds that can be utilizedinclude trimethylaluminum, triethylaluminum, triisobutylaluminum,tri-n-propylaluminum, triisopropylaluminum, tri-n-butylaluminum,tri-t-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum,tricyclohexylaluminum, triphenylaluminum, tri-p-tolylaluminum,tribenzylaluminum, trineopentylaluminum,tris(1-methylcyclopentyl)aluminum, tris(2,6-dimethylphenyl)aluminum,diethylphenylaluminum, diethyl-p-tolylaluminum, diethylbenzylaluminum,ethyldiphenylaluminum, ethyldi-p-tolylaluminum, ethyldibenzylaluminum,diethylaluminum hydride, di-n-propylaluminum hydride,diisopropylaluminum hydride, di-n-butylaluminum hydride,diisobutylaluminum hydride, di-n-octylaluminum hydride, diphenylaluminumhydride, di-p-tolylaluminum hydride, dibenzylaluminum hydride,phenylethylaluminum hydride, phenyl-n-propylaluminum hydride,phenylisopropylaluminum hydride, phenyl-n-butylaluminum hydride,phenylisobutylaluminum hydride, phenyl-n-octylaluminum hydride,p-tolylethylaluminum hydride, p-tolyl-n-propylaluminum hydride,p-tolylisopropylaluminum hydride, p-tolyl-n-butylaluminum hydride,p-tolylisobutylaluminum hydride, p-tolyl-n-octylaluminum hydride,benzylethylaluminum hydride, benzyl-n-propylaluminum hydride,benzylisopropylaluminum hydride, benzyl-n-butylaluminum hydride,benzylisobutylaluminum hydride, and benzyl-n-octylaluminum hydride,ethylaluminum dihydride, n-propylaluminum dihydride, isopropylaluminumdihydride, n-butylaluminum dihydride, isobutylaluminum dihydride,-octylaluminum dihydride, dimethylaluminum hexanoate, diethylaluminumoctoate, diisobutylaluminum 2-ethylhexanoate, dimethylaluminumneodecanoate, diethylaluminum stearate, diisobutylaluminum oleate,methylaluminum bis(hexanoate), ethylaluminum bis(octoate),isobutylaluminum bis(2-ethylhexanoate), methylaluminumbis(neodecanoate), ethylaluminum bis(stearate), isobutylaluminumbis(oleate), dimethylaluminum methoxide, diethylaluminum methoxide,diisobutylaluminum methoxide, dimethylaluminum ethoxide, diethylaluminumethoxide, diisobutylaluminum ethoxide, dimethylaluminum phenoxide,diethylaluminum phenoxide, diisobutylaluminum phenoxide, methylaluminumdimethoxide, ethylaluminum dimethoxide, isobutylaluminum dimethoxide,methylaluminum diethoxide, ethylaluminum diethoxide, isobutylaluminumdiethoxide, methylaluminum diphenoxide, ethylaluminum diphenoxide,isobutylaluminum diphenoxide, tris(fluromethyl)aluminum, and the like,and mixtures thereof.

Another class of organoaluminum compounds that can be utilized to formingredient (c) of the catalyst composition of this invention isaluminoxanes. Aluminoxanes are well known in the art and compriseoligomeric linear aluminoxanes that can be represented by the generalformula:

and oligomeric cyclic aluminoxanes that can be represented by thegeneral formula:

where x is an integer of 1 to about 100, preferably about 10 to about50; y is an integer of 2 to about 100, preferably about 3 to about 20;and each R⁴, which may be the same or different, is a mono-valentorganic group that is attached to the aluminum atom via a carbon atom.Preferably, each R⁴ is a hydrocarbyl group such as, but not limited to,alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl,substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl,alkaryl, and alkynyl groups, with each group preferably containing from1 carbon atoms, or the appropriate minimum number of carbon atoms toform the group, up to about 20 carbon atoms. These hydrocarbyl groupsmay contain heteroatoms such as, but not limited to, nitrogen, oxygen,silicon, sulfur, and phosphorus atoms. It should be noted that thenumber of moles of the aluminoxane as used in this application refers tothe number of moles of the aluminum atoms rather than the number ofmoles of the oligomeric aluminoxane molecules. This convention iscommonly employed in the art of catalysis utilizing aluminoxanes.

In general, aluminoxanes can be prepared by reactingtrihydrocarbylaluminum compounds with water. This reaction can beperformed according to known methods, such as (1) a method in which thetrihydrocarbylaluminum compound is dissolved in an organic solvent andthen contacted with water, (2) a method in which thetrihydrocarbylaluminum compound is reacted with water of crystallizationcontained in, for example, metal salts, or water adsorbed in inorganicor organic compounds, and (3) a method in which thetrihydrocarbylaluminum compound is added to the monomer or monomersolution that is to be polymerized, and then water is added.

Some specific examples of suitable aluminoxane compounds that can beutilized include methylaluminoxane (MAO), modified methylaluminoxane(MMAO), ethylaluminoxane, n-propylaluminoxane, isopropylaluminoxane,n-butylaluminoxane, n-hexylaluminoxane, n-octylaluminoxane,isobutylaluminoxane, t-butylaluminoxane, neopentylaluminoxane,cyclohexylaluminoxane, 1-methylcyclopentylaluminoxane,2,6-dimethylphenylaluminoxane, and the like, and mixtures thereof.Isobutylaluminoxane is particularly useful on the grounds of itsavailability and its solubility in aliphatic and cycloaliphatichydrocarbon solvents. Modified methylaluminoxane can be formed bysubstituting about 20-80% of the methyl groups of methylaluminoxane withC₂ to C₁₂ hydrocarbyl groups, preferably with isobutyl groups, by usingtechniques known to those skilled in the art.

The catalyst composition of this invention has very high catalyticactivity over a wide range of total catalyst concentrations and catalystingredient ratios. The polymers having the most desirable properties,however, are obtained within a narrower range of total catalystconcentrations and catalyst ingredient ratios. Further, it is believedthat the three catalyst ingredients (a), (b), and (c) can interact toform an active catalyst species. Accordingly, the optimum concentrationfor any one catalyst ingredient is dependent upon the concentrations ofthe other catalyst ingredients. The molar ratio of the hydrogenphosphite to the iron-containing compound (P/Fe) can be varied fromabout 0.5:1 to about 50:1, more preferably from about 1:1 to about 25:1,and even more preferably from about 2:1 to about 10:1. The molar ratioof the aluminum in the blend of two or more organoaluminum compounds tothe iron-containing compound (Al/Fe) can be varied from about 1:1 toabout 100:1, more preferably from about 3:1 to about 50:1, and even morepreferably from about 5:1 to about 25:1.

As discussed above, the catalyst composition of the present invention ispreferably formed by combining the three catalyst ingredients (a), (b),and (c). Although an active catalyst species is believed to result fromthis combination, the degree of interaction or reaction between thevarious ingredients or components is not known with any great degree ofcertainty. Therefore, it should be understood that the term “catalystcomposition” has been employed to encompass a simple mixture of theingredients, a complex of the various ingredients that is caused byphysical or chemical forces of attraction, a chemical reaction productof the ingredients, or a combination of the foregoing.

The catalyst composition of the present invention can be formed bycombining or mixing the catalyst ingredients or components by using, forexample, one of the following methods.

First, the catalyst composition may be formed in situ by adding thethree catalyst ingredients to a solution containing monomer and solvent,or simply bulk monomer, in either a stepwise or simultaneous manner.When adding the catalyst ingredients in a stepwise manner, the sequencein which the ingredients are added is not critical. Preferably, however,the iron-containing compound is added first, followed by the hydrogenphosphite, and finally followed by the blend of two or moreorganoalurninum compounds.

Second, the three catalyst ingredients may be pre-mixed outside thepolymerization system at an appropriate temperature, which is generallyfrom about −20° C. to about 80° C., and the resulting catalystcomposition is then added to the monomer solution.

Third, the catalyst composition may be pre-formed in the presence ofmonomer. That is, the three catalyst ingredients are pre-mixed in thepresence of a small amount of monomer at an appropriate temperature,which is generally from about −20° C. to about 80° C. The amount ofmonomer that is used for the catalyst pre-forming can range from about 1to about 500 moles per mole of the iron-containing compound, andpreferably should be from about 4 to about 100 moles per mole of theiron-containing compound. The resulting catalyst composition is thenadded to the remainder of the monomer that is to be polymerized.

Fourth, the catalyst composition may be formed by using a two-stageprocedure. The first stage involves combining the iron-containingcompound and the blend of two or more organoaluminum compounds in thepresence of a small amount of monomer at an appropriate temperature,which is generally from about −20° C. to about 80° C. In the secondstage, the foregoing reaction mixture and the hydrogen phosphite arecharged in either a stepwise or simultaneous manner to the remainder ofthe monomer that is to be polymerized.

Fifth, an alternative two-stage procedure may also be employed. Aniron-ligand complex is first formed by pre-combining the iron-containingcompound with the hydrogen phosphite. Once formed, this iron-ligandcomplex is then combined with the blend of two or more organoaluminumcompounds to form the active catalyst species. The iron-ligand complexcan be formed separately or in the presence of the monomer that is to bepolymerized. This complexation reaction can be conducted at anyconvenient temperature at normal pressure, but for an increased rate ofreaction, it is preferable to perform this reaction at room temperatureor above. The temperature and time used for the formation of theiron-ligand complex will depend upon several variables including theparticular starting materials and the solvent employed. Once formed, theiron-ligand complex can be used without isolation from the complexationreaction mixture. If desired, however, the iron-ligand complex may beisolated from the complexation reaction mixture before use.

With respect to the catalyst ingredient (c), i.e., the blend of two ormore organoaluminum compounds, it is advantageous to preform this blendby combining two or more organoaluminum compounds prior to mixing theblend with the other catalyst ingredients and the monomers that are tobe polymerized. Nevertheless, the blend of two or more organoaluminumcompounds can also be formed in situ. That is, the two or moreorganoaluminum compounds are combined at the time of polymerization inthe presence of the other catalyst ingredients and the monomers that areto be polymerized.

When a solution of the iron-based catalyst composition or one or more ofthe catalyst ingredients is prepared outside the polymerization systemas set forth in the foregoing methods, an organic solvent or carrier ispreferably employed. Useful solvents include hydrocarbon solvents suchas aromatic hydrocarbons, aliphatic hydrocarbons, and cycloaliphatichydrocarbons. Non-limiting examples of aromatic hydrocarbon solventsinclude benzene, toluene, xylenes, ethylbenzene, diethylbenzene,mesitylene, and the like. Non-limiting examples of aliphatic hydrocarbonsolvents include n-pentane, n-hexane, n-heptane, n-octane, n-nonane,n-decane, isopentane, isohexanes, isopentanes, isooctanes,2,2-dimethylbutane, petroleum ether, kerosene, petroleum spirits, andthe like. Non-limiting examples of cycloaliphatic hydrocarbon solventsinclude cyclopentane, cyclohexane, methylcyclopentane,methylcyclohexane, and the like. Commercial mixtures of the abovehydrocarbons may also be used. For environmental reasons, aliphatic andcycloaliphatic solvents are highly preferred. The foregoing organicsolvents may serve to dissolve the catalyst composition or ingredients,or the solvent may simply serve as a carrier in which the catalystcomposition or ingredients may be suspended.

As described above, the catalyst composition utilized in the presentinvention exhibits a very high catalytic activity for the polymerizationof conjugated dienes. Some specific examples of conjugated diene thatcan be polymerized include 1,3-butadiene, isoprene, 1,3-pentadiene,1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene, and 2,4-hexadiene. Mixtures of two or moreconjugated dienes may also be utilized in co-polymerization. Thepreferred conjugated dienes are 1,3-butadiene, isoprene, 1,3-pentadiene,and 1,3-hexadiene. The most preferred monomer is 1,3-butadiene inasmuchas the catalyst composition of this invention advantageously has veryhigh catalytic activity and stereoselectivity for polymerizing1,3-butadiene into syndiotactic 1,2-polybutadiene, and, as noted above,the melting temperature of the syndiotactic 1,2-polybutadiene can beadjusted.

The production of conjugated diene polymers, such as syndiotactic1,2-polybutadiene, according to this invention is accomplished bypolymerizing conjugated diene monomers in the presence of acatalytically effective amount of the foregoing catalyst composition.There are available a variety of methods for bringing the ingredients ofthe catalyst composition into contact with conjugated dienes asdescribed above. To understand what is meant by a catalyticallyeffective amount, it should be understood that the total catalystconcentration to be employed in the polymerization mass depends on theinterplay of various factors such as the purity of the ingredients, thepolymerization temperature, the polymerization rate and conversiondesired, and many other factors. Accordingly, specific total catalystconcentration cannot be definitively set forth except to say thatcatalytically effective amounts of the respective catalyst ingredientsshould be used. Generally, the amount of the iron-containing compoundused can be varied from about 0.01 to about 2 mmol per 100 g ofconjugated diene monomers, with a more preferred range being from about0.02 to about 1.0 mmol per 100 g of conjugated diene monomers, and amost preferred range being from about 0.05 to about 0.5 mmol per 100 gof conjugated diene monomers.

The polymerization of conjugated diene monomers according to thisinvention is preferably carried out in an organic solvent as thediluent. Accordingly, a solution polymerization system may be employedin which both the monomer to be polymerized and the polymer formed aresoluble in the polymerization medium. Alternatively, a precipitationpolymerization system may be employed by choosing a solvent in which thepolymer formed is insoluble. In both cases, an amount of the organicsolvent in addition to the organic solvent that may be used in preparingthe iron-based catalyst composition is usually added to thepolymerization system. The additional organic solvent may be either thesame as or different from the organic solvent contained in the catalystsolutions. It is normally desirable to select an organic solvent that isinert with respect to the catalyst composition employed to catalyze thepolymerization. Suitable types of organic solvents that can be utilizedas the diluent include, but are not limited to, aliphatic,cycloaliphatic, and aromatic hydrocarbons. Some representative examplesof suitable aliphatic solvents include n-pentane, n-hexane, n-heptane,n-octane, n-nonane, n-decane, isopentane, isohexanes, isopentanes,isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene, petroleumspirits, and the like. Some representative examples of suitablecycloaliphatic solvents include cyclopentane, cyclohexane,methylcyclopentane, methylcyclohexane, and the like. Some representativeexamples of suitable aromatic solvents include benzene, toluene,xylenes, ethylbenzene, diethylbenzene, mesitylene, and the like.Commercial mixtures of the above hydrocarbons may also be used. Forenvironmental reasons, aliphatic and cycloaliphatic solvents are highlypreferred.

The concentration of conjugated diene monomers to be polymerized is notlimited to a special range. Generally, however, it is preferred that theconcentration of the monomer present in the polymerization medium at thebeginning of the polymerization be in a range of from about 3% to about80% by weight, more preferably from about 5% to about 50% by weight, andeven more preferably from about 10% to about 30% by weight.

The polymerization of conjugated diene monomers according to thisinvention may also be carried out by means of bulk polymerization, whichrefers to a polymerization environment where no solvents are employed.Bulk polymerization can be conducted either in a condensed liquid phaseor in a gas phase.

In performing the polymerization of conjugated diene monomers accordingto this invention, a molecular weight regulator may be employed tocontrol the molecular weight of the conjugated diene polymers to beproduced. As a result, the scope of the polymerization system can beexpanded in such a manner that it can be used for the production ofconjugated diene polymers having a wide range of molecular weights.Suitable types of molecular weight regulators that can be utilizedinclude, but are not limited to, α-olefins such as ethylene, propylene,1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene; accumulateddiolefins such as allene and 1,2-butadiene; nonconjugated diolefins suchas 1,6-octadiene, 5-methyl-1,4-hexadiene, 1,5-cyclooctadiene,3,7-dimethyl-1,6-octadiene, 1,4-cyclohexadiene, 4-vinylcyclohexene,1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,6-heptadiene,1,2-divinylcyclohexane, 5-ethylidene-2-norbornene,5-methylene-2-norbornene, 5-vinyl-2-norbornene, dicyclopentadiene, and1,2,4-trivinylcyclohexane; acetylenes such as acetylene, methylacetyleneand vinylacetylene; and mixtures thereof. The amount of the molecularweight regulator used, expressed in parts per hundred parts by weight ofthe conjugated diene monomers (phm), is from about 0.01 to about 10 phm,preferably from about 0.02 to about 2 phm, and more preferably fromabout 0.05 to about 1 phm.

The molecular weight of the conjugated diene polymers to be produced canalso be effectively controlled by polymerizing conjugated diene monomersin the presence of hydrogen gas. In this case, the preferable partialpressure of hydrogen gas is within the range of about 0.01 to about 50atmospheres.

The polymerization of conjugated diene monomers according to thisinvention may be carried out as a batch process, a continuous process,or even a semi-continuous process. In the semi-continuous process,monomer is intermittently charged as needed to replace that monomeralready polymerized. In any case, the polymerization is desirablyconducted under anaerobic conditions by using an inert protective gassuch as nitrogen, argon or helium, with moderate to vigorous agitation.The polymerization temperature employed in the practice of thisinvention may vary widely from a low temperature, such as −10° C. orbelow, to a high temperature such as 100° C. or above, with a preferredtemperature range being from about 20° C. to about 90° C. The heat ofpolymerization may be removed by external cooling, cooling byevaporation of the monomer or the solvent, or a combination of the twomethods. Although the polymerization pressure employed may vary widely,a preferred pressure range is from about 1 atmosphere to about 10atmospheres.

Once a desired conversion is achieved, the polymerization can be stoppedby the addition of a polymerization terminator that inactivates thecatalyst. Typically, the terminator employed is a protic compound, whichincludes, but is not limited to, an alcohol, a carboxylic acid, aninorganic acid, water, or a mixture thereof. An antioxidant such as2,6-di-tert-butyl-4-methylphenol may be added along with, before orafter the addition of the terminator. The amount of the antioxidantemployed is preferably in the range of 0.2% to 1% by weight of thepolymer product. When the polymerization reaction has been stopped, thepolymer can be recovered from the polymerization mixture by conventionalprocedures of desolventization and drying. For instance, the polymer maybe isolated from the polymerization mixture by coagulation of thepolymerization mixture with an alcohol such as methanol, ethanol, orisopropanol, or by steam distillation of the solvent and the unreactedmonomer, followed by filtration. The polymer product is then dried toremove residual amounts of solvent and water.

As noted above, a preferred embodiment of this invention is directedtoward a process for the synthesis of crystalline conjugated dienepolymers such as syndiotactic 1,2-polybutadiene. Advantageously, themelting temperature of the resulting crystalline conjugated dienepolymers produced according to this invention can be manipulated byemploying a blend of two or more organoaluminum compounds that havedistinct steric hindrance. In general, it has been found that the use ofa sterically hindered organoaluminum compound within the iron-basedcatalyst composition gives rise to a polymer having a relatively highmelting temperature, and that the use of a sterically non-hinderedorganoaluminum compound within the iron-based catalyst composition givesrise to a polymer having a relatively low melting temperature.Surprisingly, it has been discovered that by employing a blend ofsterically dissimilar organoaluminum compounds, one can tailor themelting temperature of the resulting polymer. In other words, by using ablend of a sterically hindered organoaluminum compound that yields apolymer having a relatively high melting temperature and a stericallynon-hindered organoaluminum compound that yields a polymer having arelatively low melting temperature, one can obtain a polymer whosemelting temperature is somewhere between the relatively high andrelative low temperatures.

For example, when an acyclic hydrogen phosphite is employed within theiron-based catalyst composition, the use of a sterically non-hinderedorganoaluminum compound generally yields a syndiotactic1,2-polybutadiene polymer having amelting temperature of from about 90°C. to about 130° C. On the other hand, the use of a sterically hinderedorganoaluminum compound generally yields a syndiotactic1,2-polybutadiene polymer having a melting temperature of from about180° C. to about 210° C. By using a blend of a sterically hinderedorganoaluminum compound and a sterically non-hindered organoaluminumcompound, one can obtain a syndiotactic 1,2-polybutadiene polymer whosemelting temperature is somewhere between about 90° C. and about 210° C.when an acyclic hydrogen phosphite is used within the catalystcomposition. Advantageously, the process of this invention allows forthe synthesis of syndiotactic 1,2-polybutadiene having a meltingtemperature from about 130° C. to about 170° C., more advantageouslyfrom about 140° C. to about 170° C., and even more advantageously fromabout 150° C. to about 160° C.

Moreover, the desired melting temperature of the resulting crystallineconjugated diene polymer can be achieved by adjusting the molar ratio ofthe hindered to non-hindered organoaluminum compounds. In general, themelting temperature of the resulting polymer can be increased byincreasing the molar ratio of the hindered to non-hinderedorganoaluminum compounds. Likewise, the melting temperature of theresulting polymer can be decreased by decreasing the molar ratio of thehindered to non-hindered organoaluminum compounds.

In addition to adjusting the molar ratio of the hindered to non-hinderedorganoaluminum compounds, the melting temperatures of the resultingcrystalline conjugated diene polymer can be manipulated by selectingcertain organoaluminum compounds within the class of hindered compounds,by selecting certain organoaluminum compounds within the class ofnon-hindered compounds, or by selecting one or more from each class. Theselected organoaluminum compounds are then combined to form ingredient(c) of the catalyst composition.

It has also been found that the molecular weight, 1,2-linkage content,and syndiotacticity of the syndiotactic 1,2-polybutadiene can beincreased by increasing the molar ratio of the hindered to non-hinderedorganoaluminum compounds within the blend two or more stericallydistinct organoaluminum compounds.

The syndiotactic 1,2-polybutadiene produced with the catalystcomposition of this invention has many uses. It can be blended withvarious rubbers in order to improve the properties thereof. For example,it can be incorporated into elastomers in order to improve the greenstrength of those elastomers, particularly in tires. The supporting orreinforcing carcass of tires is particularly prone to distortion duringtire building and curing procedures. For this reason, the incorporationof the syndiotactic 1,2-polybutadiene into rubber compositions that areutilized in the supporting carcass of tires has particular utility inpreventing or minimizing this distortion. In addition, the incorporationof the syndiotactic 1,2-polybutadiene into tire tread compositions canreduce the heat build-up and improve the tear and wear characteristicsof tires. The syndiotactic 1,2-polybutadiene is also useful in themanufacture of films and packaging materials and in many moldingapplications.

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested as described in theGeneral Experimentation Section disclosed hereinbelow. The examplesshould not, however, be viewed as limiting the scope of the invention.The claims will serve to define the invention.

GENERAL EXPERIMENTATION EXAMPLE 1

An oven-dried 1-liter glass bottle was capped with a self-sealing rubberliner and a perforated metal cap. After the bottle was thoroughly purgedwith a stream of dry nitrogen gas, the bottle was charged with 73 g ofhexanes and 177 g of a 1,3-butadiene/hexanes blend containing 28.3% byweight of 1,3-butadiene. The following catalyst ingredients were addedto the bottle in the following order: (1) 0.050 mmol of iron(III)2-ethylhexanoate, (2) 0.20 mmol of bis(2-ethylhexyl) hydrogen phosphite,and (3) 0.75 mmol of triethylaluminum. The bottle was tumbled for 4hours in a water bath maintained at 50° C. The polymerization wasterminated by addition of 10 mL of isopropanol containing 1.0 g of2,6-di-tert-butyl-4-methylphenol. The polymerization mixture wascoagulated with 3 liters of isopropanol. The resulting syndiotactic1,2-polybutadiene was isolated by filtration and dried to a constantweight under vacuum at 60° C. The yield of the polymer was 45.3 g (91%).As measured by differential scanning calorimetry (DSC), the polymer hada melting temperature of 133° C. The ¹H and ¹³C nuclear magneticresonance (NMR) analysis of the polymer indicated a 1,2-linkage contentof 88.3% and a syndiotacticity of 76.1%. As determined by gel permeationchromatography (GPC), the polymer had a weight average molecular weight(M_(w)) of 512,000, a number average molecular weight (M_(n)) of226,000, and a polydispersity index (M_(w)/M_(n)) of 2.3. The monomercharge, the amounts of the catalyst ingredients, the polymer yield, andthe properties of the resulting syndiotactic 1,2-polybutadiene aresummarized in Table I.

TABLE I Example No. 1 2 3 4 5 Hexanes (g)  73  73  73  73  73 28.3%1,3-Bd/hexanes (g) 177 177 177 177 177 Fe(2-EHA)₃ (mmol)  0.050  0.050 0.050  0.050  0.050 HP(O)(OCH₂CH(Et)(CH₂)₃CH₃)₂ (mmol)  0.20  0.20 0.20  0.20  0.20 i-Bu₃Al/Et₃Al molar ratio 0:100 30:70 50:50 70:30100:0 Total AlR₃ (mmol)  0.75  0.75  0.75  0.75  0.75 Fe/P/Al molarratio 1:4:15 1:4:15 1:4:15 1:4:15 1:4:15 Polymer yield (%) after 4 hr at50° C.  91  98  97  98  96 Melting temperature (° C.) 133 144 157 179188 M_(w) 512,000 580,000 629,000 719,000 773,000 M_(n) 226,000 264,000299,000 359,000 381,000 M_(w)/M_(n)  2.3  2.2  2.1  2.0  2.0 1,2-Linkagecontent (%)  87.3  88.0  89.2  89.8  90.9 Syndiotacticity (%)  76.9 81.0  87.5  90.1  93.3

Examples 2-5

In Examples 2-5, the procedure described in Example 1 was repeatedexcept that triisobutylaluminum/triethylaluminum mixtures having variousmolar ratios, i.e., 30:70, 50:50, 70:30, and 100:0 were substituted forthe triethylaluminum. Table I summarizes the monomer charge, amounts ofthe catalyst ingredients, polymer yields, and the properties of theresulting syndiotactic 1,2-polybutadiene produced in each example.

As shown in Table I, the melting temperature, molecular weight,1,2-linkage content, and syndiotacticity of the syndiotactic1,2-polybutadiene can be increased by increasing the molar ratio oftriisobutylaluminum to triethylaluminum.

Examples 6-10

In Examples 6-10, the procedure described in Example 1 was repeatedexcept that triisobutylaluminum/tri-n-butylaluminum mixtures havingvarious molar ratios, i.e., 0:100, 30:70, 50:50, 70:30, and 100:0 weresubstituted for the triethylaluminum. The monomer charge, the amounts ofthe catalyst ingredients, polymer yields, and the properties of theresulting syndiotactic 1,2-polybutadiene are summarized in Table II.

TABLE II Example No. 6 7 8 9 10 Hexanes (g)  73  73  73  73  73 28.3%1,3-Bd/hexanes (g) 177 177 177 177 177 Fe(2-EHA)₃ (mmol)  0.050  0.050 0.050  0.050  0.050 HP(O)(OCH₂CH(Et)(CH₂)₃CH₃)₂ (mmol)  0.20  0.20 0.20  0.20  0.20 i-Bu₃Al/n-Bu₃Al molar ratio 0:100 30:70 50:50 70:30100:0 Total AlR₃ (mmol)  0.75  0.75  0.75  0.75  0.75 Fe/P/Al molarratio 1:4:15 1:4:15 1:4:15 1:4:15 1:4:15 Polymer yield (%) after 4 hr at50° C.  96  98  99  98  96 Melting temperature (° C.) 133 146 158 171188 M_(w) 424,000 561,000 625,000 700,000 773,000 M_(n) 191,000 278,000298,000 320,000 381,000 M_(w)/M_(n)  2.2  2.0  2.1  2.2  2.0 1,2-Linkagecontent (%)  87.0  88.2  89.6  90.2  90.9 Syndiotacticity (%)  77.7 81.4  87.0  89.6  93.3

As shown in Table II, the melting temperature, molecular weight,1,2-linkage content, and syndiotacticity of the syndiotactic1,2-polybutadiene can be increased by increasing the molar ratio oftriisobutylaluminum to tri-n-butylaluminum.

Various modifications and alterations that do not depart from the scopeand spirit of this invention will become apparent to those skilled inthe art. This invention is not to be duly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A catalyst composition that is the combination ofor reaction product of ingredients comprising: (a) an iron-containingcompound; (b) a hydrogen phosphite; and (c) a blend of two or moresterically distinct organoaluminum compounds, where said blend of two ormore sterically distinct organoaluminum compounds includes at least onesterically hindered organoaluminum compound and at least one stericallynon-hindered organoaluminum compound.
 2. The catalyst compound of claim1, where the at least one sterically hindered organoaluminum compound istriisopropylaluminum, triisobutylaluminum, tri-t-butylaluminum,trineopentylaluminum, tricyclohexylaluminum,tris(1-methylcyclopentyl)aluminum, tris(2,6-dimethylphenyl)aluminum, ormixtures thereof.
 3. The catalyst composition of claim 1, where the atleast one sterically non-hindered organoaluminum compound istrimethylaluminum, triethylaluminum, tri-n-propylaluminum,tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, ormixtures thereof.
 4. The catalyst composition of claim 1, where the atleast one sterically hindered organoaluminum compound isisopropylaluminoxane, isobutylaluminoxane, t-butylaluminoxane,neopentylaluminoxane, cyclohexylaluminoxane,1-methylcyclopentylaluminoxane, 2,6-dimethylphenylaluminoxane, ormixtures thereof.
 5. The catalyst composition of claim 1, where the atleast one sterically non-hindered organoaluminum compound ismethylaluminoxane, ethylaluminoxane, n-propylaluminoxane,n-butylaluminoxane, n-hexylaluminoxane, n-octylaluminoxane, or mixturesthereof.
 6. The catalyst composition of claim 1, where theiron-containing compound includes an iron carboxylate, an ironcarbamate, an iron dithiocarbamate, and iron xanthate, an ironβ-diketonate, an iron alkoxide, an iron aryloxide, and an organoironcompound.
 7. The catalyst composition of claim 1, where the hydrogenphosphite is selected from compounds that are defined by the one or moreof the following keto-enol toutomeric structures:

where R¹ and R², which may be the same or different, are mono-valentorganic groups, and R³ is a divalent organic group.
 8. The catalystcomposition of claim 1, wherein the iron atom of the iron-containingcompound has an oxidation state of 0, +2, or +4.
 9. The catalystcomposition of claim 7, where the hydrogen phosphite is an acylichydrogen phosphite defined by the following keto-enol tautomericstructure:

where R¹ and R², which may be the same or different, are mono-valentorganic groups.
 10. The catalyst composition of claim 1, where the molarratio of the hydrogen phosphite to the iron-containing compound is fromabout 0.5:1 to about 50:1, and the molar ratio of the aluminum in theblend of two or more organoaluminum compounds to the iron-containingcompound is from about 1:1 to about 100:1.
 11. The catalyst compositionof claim 10, where the molar ratio of the hydrogen phosphite to theiron-containing compound is from about 1:1 to about 25:1, and the molarratio of the aluminum in the blend of two or more organoaluminumcompounds to the iron-containing compound is from about 3:1 to about50:1.
 12. The catalyst composition of claim 10, where the molar ratio ofthe hydrogen phosphite to the iron-containing compound is from about 2:1to about 10:1, and the molar ratio of the aluminum in the blend of twomore organoaluminum compounds to the iron-containing compound is fromabout 5:1 to about 25:1.
 13. A catalyst composition formed by a processcomprising the step of combining: (a) an iron-containing compound; (b) ahydrogen phosphite; and (c) a blend of two or more sterically distinctorganoaluminum compounds, where said blend of two or more stericallydistinct organoaluminum compounds includes at least one stericallyhindered organoaluminum compound and at least one stericallynon-hindered organoaluminum compound.
 14. The catalyst composition ofclaim 13, where said iron-containing compound, hydrogen phosphite, andblend of two or more sterically distinct organoaluminum compounds arecombined in the presence of 1,3-butadiene monomer.
 15. The catalystcomposition of claim 13, where the at least one sterically hinderedorganoaluminum compound is triisopropylaluminum, triisobutylaluminum,tri-t-butylaluminum, trineopentylaluminum, tricyclohexylaluminum,tris(1-methylcyclopentyl)aluminum, tris(2,6-dimethylphenyl)aluminum, ormixtures thereof.
 16. The catalyst compound of claim 13, where the atleast one sterically non-hindered organoaluminum compound istrimethylaluminum, triethylaluminum, tri-n-propylaluminum,tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, or amixture thereof.
 17. The catalyst compound of claim 13, where the atleast one sterically hindered organoaluminum compound isisopropylaluminoxane, isobutylaluminoxane, t-butylaluminoxane,neopentylaluminoxane, cyclohexylaluminoxane,1-methylcyclopentylaluminoxane, 2,6-dimethylphenylaluminoxane, ormixtures thereof.
 18. The catalyst composition of claim 13, where the atleast one sterically non-hindered organoaluminum compound ismethylaluminoxane, ethylaluminoxane, n-propylaluminoxane,n-butylaluminoxane, n-hexylaluminoxane, n-octylaluminoxane, or mixturesthereof.